Tissue engineering is an area of intense effort today in the field of biomedical sciences. The development of methods of tissue engineering and replacement is of particular importance in tissues that are unable to heal or repair themselves, such as articular cartilage. Articular cartilage is a unique avascular, aneural and alymphatic load-bearing live tissue, which is supported by the underlying subchondral bone plate. Articular cartilage damage is common and does not normally self-repair. Challenges related to the cellular component of an engineered tissue include cell sourcing, as well as expansion and differentiation. Findings of recent well-designed studies suggest that autologous chondrocyte implantation is the most efficacious technique for repairing symptomatic full-thickness hyaline articular cartilage defects, which engender a demand for cell-based strategies for cartilage repair. Further studies have also attempted to engineer cartilage via the combination of biodegradable or biocompatible scaffolds with differentiated chondrocytes. According to these studies, it is unlikely that a sufficient supply of differentiated chondrocytes will be available for clinical applications.
Numerous studies have focused on cell sources from tissues other than cartilage for cartilage tissue engineering. Embryonic stem (ES) cells represent a valuable source for this purpose. The application of ES cells in this area, however, is still limited particularly because of ethical considerations. A number of researchers have investigated various adult tissues including bone marrow, muscle, and adipose tissue as alternative cell sources for cartilage tissue engineering. However, autologous procurement of these tissues has potential limitations.
Skin is the largest organ in the body and is relatively easily accessible with minimal insult to the donor. The skin dermis is considered, therefore, one of the best autologous source organs to isolate stem/progenitor cells for future therapeutic applications not only in the replacement of skin, but also as an alternative cell source for several other organs outside of skin. Recently accumulating evidence indicates that skin dermis contains cells that can generate multiple lineages including neurons, glia, smooth muscle cells and adipocytes. Thus, cells from the skin dermis may prove to be a useful alternative cell source for articular cartilage tissue engineering. There is increasing evidence which suggests that human dermal fibroblasts cultured with demineralized bone powder acquire a chondroblast phenotype and express cartilage-specific matrix proteins. However, evidence shows that there are several types of fibroblasts in the skin dermis with different functions, which suggests the limitation of these cells. Although the existence of chondrogenic precursor cells in skin dermis has long been postulated, thus far it has been impossible to induce these heterogeneous cells to differentiate into chondrocytes exclusively, either in vivo or in vitro.
Previous studies using dermal fibroblasts showed that demineralized bone powder could induce the formation of colonies exhibiting a chondrocytic phenotype. However, no further evidence exists to show whether these chondroinduced cells can be considered to originate from stem cells, fully mature fibroblasts, or a dermal subpopulation of cells with latent chondrogenic potential. Although a number of researchers have investigated techniques to isolate subpopulations from the dermis for different purposes, none of these subpopulations has been isolated specifically for cartilage regeneration. Thus, there is an absence of well defined and efficient protocols for the selective isolation and proliferation of dermis-derived cells, followed by directing their differentiation into the chondrogenic lineage in vitro.